Thor is the Asgardian God of Thunder and the son of Odin, the All-Father of Asgard , and the Elder Earth-Goddess Gaea. Combining the power of both worlds, Thor is arguably the greatest and mightiest defender of both . Armed with his powerful enchanted hammer Mjolnir, Thor is the mightiest warrior of Asgard, a founding member of the Avengers and one of the strongest, most powerful beings on Earth.

The weight obviously does not count at all, If your worthy you lift it, so that counters the weight as an unworthy person cannot lift it at all, a paradox as the hammers weight will never be tested, the question is, how heavy is it once you are worthy and you pick it up xD

If you are worthy I believe the hammer to be virtually weightless to its weilder. However if you are not worthy then the weight of mjolnir is greater than the force that the person is applying to pick it up with.